The present invention relates to a method of and a circuit arrangement for dosing or metering in a printing machine having an ink fountain engaging a doctor roller driven by a separate motor.
The metering of printing ink according to different printing applications by means of an ink fountain provided with an ink blade adjustable by zone screws and being in adjustable engagement with an ink doctor roller which cooperates with an ink lifter roller is known since long time. To meet the general requirement for continuously increase the printing efficiency, a large number of improvements in this field have been recently developed which, however, are frequently very complicated in their design.
From the DD Pat. No. 212,475 a solution is known in which an ink film is metered on the doctor roller by the adjustment of zone screws acting on the ink blade. The ink lifter roller cyclically takes off the ink film from the doctor roller and transfers the same to the first ink distributing cylinder. The ink lift roller is oscillated by a cam roller control in such a manner that at each 2.5 rotation of the printing plate cylinder of the machine a contact with the doctor roller and the first distributing cylinder takes place. By means of an electrical control activated by a selector switch it is possible to change the rate of swinging of the ink lifter roller such that each fifth or tenth rotation of the printing plate cylinder it engages once the ink doctor roller.
By means of this known device a satisfactory ink metering for most applications is achievable. Its disadvantage, however, is the fact that the time of the engagement of the ink lifter roller is not adjustable and consequently the ink metering cannot be adjusted with sufficient sensitivity.
In an ink metering device according to DE-AS 1,761,394 the ink doctor roller is driven at a constant rotary speed ratio with respect to the printing machine and ink is transferred by an ink lifter roller onto the first ink distributing cylinder. The engagement times of the ink lifter roller on the doctor roller as well as on the first ink distributing cylinder are adjustable by means of two timing device which cooperate with a change-over device. This construction consists of a large number of component parts and is very complex in design thus resulting in high manufacturing costs. An accurate reproducibility of a previously adjusted metering is not achievable.
A device for ink metering has been also devised in which the ink is taken off by a milling roller rotating at the speed of the printing machine and being arranged at a minute distance from a swichtable ink doctor roller. An ink lifter roller picks off the ink layer from the milling roller and transfers the layer to the first ink distributing cylinder. With this device an adequate ink metering is obtained. Its disadvantage is its large cost of construction and consequently high manufacturing costs.